One benefit of the continuing innovation in microelectronics has been the widespread availability of low cost wireless telecommunications equipment. The ability to make and receive telephone calls anywhere through a small pocket-sized handset has universal appeal. However, mobile telephone users are beginning to demand services beyond basic telephony such as paging, caller identification, data and facsimile, and wireless systems are thus beginning to include the features needed to support such advanced services.
One system having these features is the so-called Global System for Mobile Communications (GSM) system and related variants such as DCS-1800 and PCS-1900. The various subsystems of a GSM system are known by certain standardized terminology, including the Mobile Station (MS), Base Station Subsystem (BSS), and the Network Switching Subsystem (NSS). In general, the BSS is responsible for maintaining transmission and reception along the radio path, and the NSS is responsible for managing landline connections. The Mobile Station (MS) is the term used to refer to the handset.
The BSS typically includes two functional machines, a Base Transceiver System (BTS) and a Base Station Controller (BSC). The BTS encompasses radio transmission and reception equipment that provides over-the-air connections to the Mobile Station (MS). Each BTS typically serves the Mobile Stations (MS) located in a small area, or cell, of the total area assigned to the service provider.
The BSC is typically a small switching system with call processing features and computational capacity. Its main role is to manage the handover of calls as a Mobile Station (MS) moves between cells. To accomplish this, the BSC performs functions such as radio frequency assignment, handover (HO), channel management (CH-MGMT), and channel measurement (MSMT). A single BSC is typically responsible for managing handover between a number of BTSs.
One consequence of the above architecture is that a number of limitations can arise. For example, as the number of BTSs is increased, the processing load on the BSC increases. This becomes particularly problematic where multiple BTSs are needed in order to serve a single cell, such as may come about in high density traffic areas where cells may need to be sectorized, that is, divided into sectors. Frequency assignments and intra-cell handovers must be made in this situation as though each sector were independent of the adjacent sectors. The BSC workload thus increases accordingly.
A more recent development is the broadband Base Transceiver System (BTS). The broadband BTS permits a greater number of radio channels to be processed efficiently in parallel. Therefore it becomes possible for a cellular service provider to deploy many more channels in a cell than was previously possible, enabling a greater number of users to be served for a given cost.
However, the use of a broadband BTS also increases the amount of data which must pass between the BTS and the BSC, in order to process the greater number of handovers. For example, measurement (MSMT) reports can be expected to be sent approximately twice per second from the Mobile Station (MS) to the BTS. The BTS in turn, must collect these reports and forward them to the BSC for processing. This in turn taxes the ability of the BSC to manage a given number of BTS's. Indeed, where before a single BSC may have been quite capable of servicing multiple cells, with broadband BTSs, it may even become necessary to have a single BSC servicing each cell.
Therefore, it is clear that when a broadband BTS is to be deployed, techniques are needed wherein the BSC functions can be more effectively implemented.